It is proposed to employ a controlled-potential column using chemically modified graphite as a support material for affinity chromatography. The surface of the graphite support will be pretreated to increase capacity and minimize non-specific adsorption. By controlling the charge and potential of a column one could affect the apparent dissociation constant of a system by electrostatic interactions, "local pH" conditions, or electrochemical oxidation and reduction on the support surface. Consequently, one could influence and control the extent of a protein-ligand interaction, which is the "heart" of affinity chromatography. It is believed that controlled-potential columns could add a new dimension to a technique that has already proven itself to be invaluable in biochemical separations. The following types of affinity chromatography will be studied employing controlled-potential columns: Covalent affinity chromatography using organomercurial compounds as ligands and alkyl-2-pyridyl disulfide residues for thiol-disulfide interchange to study the separation of thiol-containing proteins. Also, metal chelate affinity chromatography using iminodiacetic acid as the chelating group, which is complexed to various metal ions, such as, Cu2 ion, Zn2 ion, Ni2 ion, Co2 ion, Cd2 ion and Hg2 ion to study the separation of proteins containing imidazole and thiol groups.